In recent years, there has been developed a power generator which can generate electric power by utilizing variation of magnetic permeability of a magnetostrictive rod formed of a magnetostrictive material (for example, see patent document 1).
For example, this power generator includes a pair of magnetostrictive rods arranged side by side, two connecting yokes for respectively connecting one end portions and the other end portions of the pair of magnetostrictive rods with each other, coils arranged so as to respectively surround the magnetostrictive rods, an elongated back yoke arranged along the pair of magnetostrictive rods and two permanent magnets respectively arranged between each of the two connecting yokes and the back yoke to apply a bias magnetic field to the magnetostrictive rods. The back yoke is fixed to the connecting yokes through the permanent magnets. With this configuration, a magnetic field loop circulating in the magnetostrictive rods, the connecting yokes, the permanent magnets and the back yoke is formed.
When one of the connecting yokes is fixed and external force is applied to the other one of the connecting yokes in a direction perpendicular to an axial direction of the magnetostrictive rods, one of the magnetostrictive rods is deformed so as to be expanded and the other one of the magnetostrictive rods is deformed so as to be contracted. Due to these deformations, elastic energy is stored in each of the magnetostrictive rods. When the external force applied to the other one of the connecting yokes is released, the elastic energy stored in each of the magnetostrictive rods is converted into kinetic energy and the other one of the connecting yokes is vibrated. In this described power generator, when the other one of the connecting yokes is vibrated and each of the magnetostrictive rods is deformed, stress (tensile stress or compressive stress) is generated in each of the magnetostrictive rods. The stress generated in each of the magnetostrictive rods leads to variation of density of lines of magnetic force (magnetic flux density) passing through the magnetostrictive rods, that is variation of the density of the lines of magnetic force passing through the coils, thereby generating a voltage in the coils.
In the described power generator, the pair of magnetostrictive rods constitute beams facing each other. In order to improve power generation efficiency of the power generator having such a configuration, it is necessary that each of magnetostrictive rods can be sufficiently deformed in an expanding and contracting direction by the stress generated by the other one of the magnetostrictive rods and has a function of generating sufficiently large stress in the other one of the magnetostrictive rods. However, it is difficult to allow the magnetostrictive rods to satisfy these conditions. Thus, it is impossible to sufficiently improve the power generation efficiency of the power generator by using the power generator having the above configuration.